Fish vocalisation: understanding its biological role from temporal and spatial characteristics

In the shallow coastal waters of New Zealand, sounds of biological origin dominate the lower frequency spectrum of the underwater soundscape. While the sounds of urchin and snapping shrimp have been well described, those of fish are poorly understood. Utilising sound recordings taken from a reef in the Cape Rodney to Okakari Point Marine Reserve, the present study described the vocalisations of two dominant fish vocalisations, the croak and the purr. These sounds dominated the soundscape at frequencies below 500 Hz and regularly formed choruses that lasted up to 3 hours after sunset during the new moon, indicating the presence of soniferous fishes in New Zealand coastal waters. To help with the identification of soniferous fish species in field recordings, two local sound producing fish were studied in detail using 24 h sound recordings in captivity, the bigeye (Pempheris adspersa) and the bluefin gurnard (Chelidonichthys kumu). The bigeye produced a previously undescribed „pop‟ vocalisation with a source level of 116 dB re 1 μPa @ 1m. The active space of their calls was estimated (radius of 0.6 – 31.6 m) which suggests that their call may serve a group cohesion function during nocturnal foraging. The bluefin gurnard was acoustically prolific (19 sounds fish-1 h-1) and had a larger acoustic repertoire than had been previously reported. In addition to the two types of grunt vocalisations, a distinctive nocturnal vocalisation consisting of two new types of growls was described. This indicates that bluefin gurnards could be a major contributor to the ambient sound of their off-shore soft bottom habitat and that field recordings in these areas may be a useful means of investigating gurnard biology and monitoring populations. The present study has also described for the first time the bioacoustic environment of a fish aggregation device (FAD). Using a Malaysian FAD as a model, the present study showed that sounds in frequency bands typically dominated by various biological sources (500 Hz – 2000 Hz octave bands) could propagate up to 400 m during the day and to more than 1 km at dusk. Thus, suggesting FADs could be acting as a long range acoustic cue for fish. The results of this study have greatly enhanced our understanding of fish vocalisations and its significance in the underwater soundscape of New Zealand coastal waters. In addition, it has contributed to our general understanding of the contribution of the underwater soundscape to fish behaviour and orientation.